Biohack’s previous article on this subject covered a single snapshot of 123 adults that linked gut bacteria to a blood measure of how fast people age. What is new now is a wider look: a review that pulled together 41 human studies comparing the gut microbes of young people, older people and people who live to 100 or beyond1. It asks which microbes keep showing up in long-lived people, and it also shows how much the studies disagree.
What happened
The review, titled “Gut microbiome and healthy ageing: a systematic review of literature,” set out to find features of gut microbes linked with healthy aging1. A systematic review is a study of studies: researchers search the published work using fixed rules, then compare what the eligible papers found. In this case, 41 studies met the rules1.
The clearest pattern involved people aged 100 or older. Studies consistently reported more of three groups of bacteria in these centenarians: Akkermansia, Alistipes and Parabacteroides1. The authors also described distinct patterns in older adults and long-lived people more generally1.
Beyond which microbes were present, the review looked at what they appear to do. It found differences in chemical work tied to breaking down amino acids (the building blocks of protein), making vitamins, and processes that may be linked to the immune system, inflammation and the strength of the gut lining1.
The evidence so far
Gut microbes are a mix of bacteria, archaea, viruses, parasites and fungi living in the large intestine1. They help digest food, shape immune responses, protect against germs, and make useful chemicals such as vitamins and short-chain fatty acids1.
The review notes that in 2023, researchers added three new items to a widely used list of the “hallmarks of ageing,” and one of them was an unhealthy shift in gut microbes, known as dysbiosis1. That state is described as having fewer kinds of microbes and more of the types that drive inflammation1. In people who age well, by contrast, the gut mix tends to stay fairly stable1.
An earlier study points in a related direction. Published in 2021 in the journal Nature Metabolism, it analyzed gut microbes and health data from more than 9,000 people aged 18 to 101, with a closer focus on over 900 older adults aged 78 to 982. Gut microbes became more unique to each person with age, while bacteria that most people share became less common2. Over a 4-year follow-up, a more unique and varied mix was linked to better survival2. The study’s lead, Tomasz Wilmanski of the Institute for Systems Biology in Seattle, said:
Interestingly, this uniqueness pattern appears to start in mid-life—40-50 years old—and is associated with a clear blood metabolomic signature, suggesting that these microbiome changes may not simply be diagnostic of healthy aging, but that they may also contribute directly to health as we age.
That quote is reported in a blog post from a supplement seller2, and Wilmanski’s “may” matters: the study measured links, not effects.
What it does not show yet
The studies in the review compared groups of people. They cannot show that any of these bacteria slow aging or that changing them would help anyone live longer.
The review itself is cautious about how consistent the picture is. It says the direction and size of age-related changes, including changes in how many kinds of microbes people carry, are highly variable1. Those changes depend on health, diet, lifestyle, medicines and which population was studied1. The included studies came from several regions, including known longevity hotspots, but the authors say geographic coverage was still limited1.
The lab methods also differed. Of the 41 studies, 24 (58.5%) used a method called 16S rRNA gene sequencing, 13 (31.7%) used shotgun metagenomics, 3 used both, and 1 used metaproteomics, which looks at proteins1. Comparing results gathered in different ways adds uncertainty about whether studies were measuring the same thing.
This leaves open the question raised by the earlier uniqueness finding: whether differences between people that are not obvious from a broad list of bacteria groups track with how they age. The sources here do not answer it.
Who is behind it
The review was highlighted by Fight Aging!, a blog that openly campaigns for new therapies aimed at the causes of aging1. The blog’s own view is that gut microbes start to change in meaningful ways as early as the mid-30s, and that data like this will form the basis for later efforts to adjust the gut’s mix to slow aspects of aging1. It adds that probiotics can change the mix only temporarily, while fecal microbiota transplants (moving stool from a donor) can change it lasting, but with little control over the result1. These are the site’s views, not findings of the review.
The 2021 survival study was supported in part by a Catalyst Award in Healthy Longevity from the National Academy of Medicine and the Longevity Consortium of the National Institute on Aging2. The post describing it comes from a company that sells probiotics2. Another explainer on this subject comes from a site that promotes gut microbiome testing3. Even that site says claims about reading “your biological age” from the gut should be viewed with extreme skepticism, and that findings in centenarians are a correlation, not a proven cause3.
How it fits the field
The broad idea behind this thread is that gut microbes may feed into “inflammaging,” the slow rise in inflammation and immune trouble with age that is tied to most common age-related diseases4. Work in germ-free mice, raised with no microbes at all, suggests ordinary gut microbes are a key cause of inflammaging, but this has not been well explored in people4. The same source notes there are very few data on how gut microbes relate to genetic markers of biological age4.
The earlier 123-person study, the 2021 survival study and this review all point to links between gut microbes and aging. None of them tested whether changing those microbes changes how people age.
What to watch next
One project to follow is based at the Carolina Population Center at the University of North Carolina. It planned to collect and analyze mouth and gut microbe samples in Add Health, a nationally representative US group of adults followed over many years, and to compare them with measures of inflammation and aging4. The project was funded by the National Institute on Aging, led by Kathleen Mullan Harris, and ran from June 2020 to March 20264. Its page lists the project as past but reports no results4.
Studies that follow the same people over time, and that use the same lab methods across groups, would help show whether these microbe patterns come before changes in health or simply reflect them.
